# Using Newton's 2nd Law to find acceleration

So this is my first time posting on here and I hope I'm doing right!

1. Homework Statement

A 75-kg snowboarder has an initial velocity of 5.0 m/s at the top of a 28 ∘ incline. After sliding down the 110-mlong incline (on which the coefficient of kinetic friction is μk = 0.18), the snowboarder has attained a velocity v. The snowboarder then slides along a flat surface (on which μk = 0.15) and comes to rest after a distance x.

Use Newton's second law to find the snowboarder's acceleration while on the incline and while on the flat surface.

F_net = ma

## The Attempt at a Solution

I already drew a free body diagram when the snowboarder is on the incline with the normal force perpendicular to the slope, the force of gravity is pointing downwards, and the force of kinetic friction is pointing parallel to the slope. I know I need to use F_net = ma but I'm still very confused on how to set it up. I'm also having trouble deciding the coordinate system to use and how it relates to finding F_net.

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PeroK
Homework Helper
Gold Member
So this is my first time posting on here and I hope I'm doing right!

1. Homework Statement

A 75-kg snowboarder has an initial velocity of 5.0 m/s at the top of a 28 ∘ incline. After sliding down the 110-mlong incline (on which the coefficient of kinetic friction is μk = 0.18), the snowboarder has attained a velocity v. The snowboarder then slides along a flat surface (on which μk = 0.15) and comes to rest after a distance x.

Use Newton's second law to find the snowboarder's acceleration while on the incline and while on the flat surface.

F_net = ma

## The Attempt at a Solution

I already drew a free body diagram when the snowboarder is on the incline with the normal force perpendicular to the slope, the force of gravity is pointing downwards, and the force of kinetic friction is pointing parallel to the slope. I know I need to use F_net = ma but I'm still very confused on how to set it up. I'm also having trouble deciding the coordinate system to use and how it relates to finding F_net.
It sounds like you have set it up. What do you have for the forces on the snowboarder? Can you calculate those?

You don't need a coordinate system as such.

It sounds like you have set it up. What do you have for the forces on the snowboarder? Can you calculate those?

You don't need a coordinate system as such.
Ok, I actually figured out how to find the acceleration while on the incline.
It was a = 9.8sin(28) - (0.18)(9.8)cos(28) which equaled 3.04 m/s^2

But now I'm having trouble figuring out how to find the acceleration while on a flat surface.

CWatters
Homework Helper
Gold Member
You don't necessarily need the acceleration on the flat. At the bottom he will have some velocity or energy that gets dissipated as he slows down.

PeroK
Homework Helper
Gold Member
Ok, I actually figured out how to find the acceleration while on the incline.
It was a = 9.8sin(28) - (0.18)(9.8)cos(28) which equaled 3.04 m/s^2

But now I'm having trouble figuring out how to find the acceleration while on a flat surface.
Isn't the flat surface easier?

In fact, isn't a flat surface just an incline with an angle of 0?

Isn't the flat surface easier?

In fact, isn't a flat surface just an incline with an angle of 0?
Ah, yes. That makes sense haha. I got the right answer. Thanks for your help!